A liquid crystal display module comprises a liquid crystal display panel (liquid crystal molecules in a liquid crystal layer can be aligned by an electric field so that an image can be displayed on the liquid crystal display panel); a backlight module, which can provide light to the liquid crystal display panel; and a shell, in which the liquid crystal display panel and the backlight module are fixed.
The liquid crystal display panel comprises a liquid crystal layer, a pair of substrates (the liquid crystal layer is arranged therebetween), and a pair of polarizers which are fixed on an outer surface of a corresponding substrate. As to an image displayed on the liquid crystal display panel, it is expected that a same display quality can be obtained when an audience watches the panel from various directions. For this purpose, many attempts have been made. For example, a liquid crystal display device in a Vertical Alignment (VA) mode and a liquid crystal display device in a Plane to Line Switching (PLS) mode have been developed. With respect to the liquid crystal display device in the VA mode, verticality of liquid crystal molecules relative to the substrate is taken advantage of. With respect to the liquid crystal display device in the PLS mode, horizontality of liquid crystal molecules relative to the substrate is taken advantage of. Since the liquid crystal molecules in the aforesaid two kinds of display devices have a similar refractive index anisotropy in different directions, the liquid crystal display device in the VA mode and the liquid crystal display device in the PLS mode both have a wide viewing angle.
In order to further improve a viewing angle performance of the display device, a metal wiring pattern and slits or protrusions made of an organic film are formed on a pixel unit so that the liquid crystal molecules can have a similar tilt angle in different directions. However, due to an influence of a fringe field on the liquid crystal molecules, an aperture ratio of the pixel unit would be reduced by the pattern, slits or protrusions. The aperture ratio refers to a ratio of an area of a pixel unit through which light from the backlight module can pass to a total area of the pixel unit. Here, the pixel unit can refer to a pixel of the liquid crystal display panel which shows a basic color.
The liquid crystal molecules are aligned in a same manner according to a same electric potential. Hence, a pre-tilt is formed in the alignment film of the substrate, so that a direction and tilt angle of liquid crystal molecules near the substrate can be fixed. The pre-tilt of the alignment film is formed by a rubbing cloth that is pre-formed on an alignment material of the substrate. However, due to contacts thereof, outside materials would be introduced to the alignment film, or electrostatic charges would be generated on the alignment film, and thus a productivity of the liquid crystal display panel would be reduced when the alignment film is formed by the rubbing cloth. Moreover, since the rubbing cloth needs to be replaced frequently, a producing time and cost would be increased.
In order to improve the productivity of the liquid crystal display panel, an optical alignment technology is introduced. According to the optical alignment technology, the pre-tilt of the alignment film is formed through a non-contact method, and no pattern, slit or protrusion is formed in the pixel region. According to the optical alignment technology, a substrate is provided with a photo-reactive material, and a tilted ultraviolet irradiates a surface of the photo-reactive material. The pre-tilt of the alignment film is formed according to the irradiation direction. Therefore, the pixel unit can be divided into several regions and ultraviolet irradiates these regions from different directions, so that the pre-tilt of the liquid crystal molecules can be formed in different directions.
The pixel unit comprises a pixel electrode that is formed on one substrate, a common electrode that is formed on the other transparent substrate spaced from the substrate on which the pixel electrode is formed, and a liquid crystal layer that is arranged between the two substrates. The pixel electrode is formed on each of the pixel units that are arranged on one substrate, and the common electrode is formed on a whole surface of the other substrate. As a result, a fringe field would be generated between edges of the pixel electrodes and the common electrode. Due to the influence of the fringe field, some liquid crystal molecules are aligned independently and are not affected by the electric potential of the pixel electrode, and the light from the backlight module is shaded by the liquid crystal molecules. As a result, a fringe field texture (FFT) would appear in this region, i.e., a normal brightness cannot be shown in this region.
The pre-tilt direction of each of the domains is matched to a polarization axis of the polarizer that is fixed on the substrate of the liquid crystal display panel. Since the pre-tilt direction of each of the domains is basically perpendicular to at least one polarizer, the light which passes through the liquid crystal molecules near a domain boundary texture (DBT) or edges of the pixel electrodes is not perpendicular to the polarization axis of the polarizer. As a result, the brightness would be reduced in the region near the domain boundary texture (DBT) or edges of the pixel electrodes.
The aperture ratio of a pixel unit is a ratio of an area of the pixel unit which has a normal brightness to a total area thereof. A light transmittance of the pixel unit refers to a ratio of the brightness of the light which passes through the pixel unit to the brightness of the light that is emitted by the backlight module before passing through the pixel unit. Due to the existence of the domain boundary texture (DBT) and the fringe field texture (FFT), the brightness of the pixel unit would be reduced, and the aperture ratio and light transmittance of the pixel unit would be reduced accordingly.
According to the optical alignment technology, the pre-tilt angle is determined by a strength of the light and the irradiation time thereof. If the pre-tilt angle is too large, the liquid crystal molecules far from the alignment film would be aligned in a wrong manner and are not in consistent with the electric potential that is applied to the pixel electrodes. Consequently, the pixel unit would have brightness higher or lower than normal brightness. A picture contrast of the liquid crystal display panel would be reduced, and a black residual image would be generated. In a black residual image phenomenon, when a signal of a black image is provided to the pixel electrode, a gray color would appear on the pixel unit.
With the popularity of large sized liquid crystal televisions (TV), the market of large sized liquid crystal TV shows a good development trend. However, during production procedure, the large sized display panel has a low utilization ratio and a high cost. Therefore, the price of the large sized liquid crystal TV is relatively high, which limits the market development thereof.
At present, the aforesaid defect is eliminated through a mother substrate technology. That is, large sized panels and small sized panels are produced together in a large substrate, so that the production cost of large sized liquid crystal TV can be greatly reduced, as shown in FIG. 1. However, due to size difference among the panels, under a same view area curing condition, the liquid crystals in the panels have different pre-tilt angles since the panels have different numbers of pixels per inch in an active area thereof, as shown in FIGS. 2 and 3.
During a traditional view area curing procedure, the liquid crystal in the view area is doped with a certain proportion of reactive liquid crystal with a high purity (phototactic monomer). This kind of liquid crystal not only has a liquid crystal nucleus as the common liquid crystal molecule, but also has one or a plurality of reactive light energy base(s) at one end thereof, such as an acrylic base. Then, an external voltage is applied between an upper substrate and a lower substrate, so that the liquid crystal molecules can have a pre-tilt angle. In different domains of one pixel, the liquid crystal molecules have different tilt directions. Next, the substrates are irradiated by ultraviolet with a certain wavelength from the thin film transistor (TFT) side, the reactive liquid crystal are polymerized into a polymer network, which can attract the liquid crystal molecules in a surface layer and enable the liquid crystal molecules to form a fixed pre-tilt angle.
The chips with different sizes have different numbers of pixels per inch in an active area thereof, and thus the chips have different light transmittances during view area curing procedure. The larger the number of pixels per inch is; the smaller the aperture area of the TFT is; the lower the light transmittance will be; and the smaller the pre-tilt angle of the liquid crystal will become. In this case, there is a risk of poor liquid crystal diffusion, as shown in FIG. 2. The smaller the number of pixels per inch is; the larger the aperture area of the TFT is; the higher the light transmittance will be; and the larger the pre-tilt angle of the liquid crystal will become. In this case, there is a risk of broken bright spots, as shown in FIG. 3.
The number of pixels per inch is a unit of image resolution. Hence, if the number of pixels per inch is high, it means that the display screen can show the image with a high density.